Are two prostrations in every rak'a fard?

Question

Is the second sajda wajib? If the imam missed one sajda, will sajda al-sahw become wajib? Also: the muqtadi missed one sajda, that is, the imam rose from the sajda and, for example, began reciting the sura; or the muqtadi missed the ruku' by the time the imam reached the second sajda — what should the muqtadi now do?

Answer

Two prostrations in every rak'a are fard; if even one is omitted, the prayer will not be valid, and sajda al-sahw will not suffice. A muqtadi who, after joining [the imam], missed the ruku' should perform the ruku' and then join the imam in the sajda; whichever sajda he joins him in, it is correct.

Source: Fatawa Mahmudiyya

Preview. The full text opens with JavaScript enabled.